1. Field of the Invention
The present invention broadly relates to correction of engine unbalance and, more particularly, is concerned with a balance weight mechanism attachable in the center of an engine shaft and angularly adjustable in small increments about the rotational axis of the shaft for correcting unbalance in the engine.
2. Description of the Prior Art
The attaching of balance weights in selected positions around a rotating device in order to balance the device is old and well known as, for example, in the balancing of automobile wheels described in U.S. Pat. No. 2,780,939 to Kellogg. Examples of other applications of balancing weights are in dynamic balancing of an industrial machine tool in U.S. Pat. No. 2,241,637 to Ernst et al and in dynamic balancing of a shaft in a bearing test machine in U.S. Pat. No. 2,439,035 to Bidwell et al.
In engines of the type having relatively large hollow tubular drive shafts, one method of intershaft unbalance correction has been to attach a balance weight to one of the bolts which normally hold the stiffener plates in the shaft together. The drawback to this method of balancing is that it is limited to very large increments of angular adjustment. For example, if four bolts are used to hold the stiffener plates, the balance weight can be angularly adjusted in ninety degree increments; if eight bolts are used the angular increment is forty-five degrees. Therefore, a need exists for an unbalance correction technique which provides greater precision in adjustment of balance weight.